With modern production methods, there is great need to be able to handle large numbers of stacked and/or nested products in an automated fashion. The term "nested" is used in this patent application to designate stacked products that have raised lips or edges, so that when the products are placed in a line, the lip or edge of a first product will overlap the bottom of a second product in front of the first product. For the rest of this patent application the term "stacked product" shall mean stacked and/or nested product.
The handling of stacked products includes the need to count products, separate the products into some sort of counted units that have a predetermined number of product in them and arrange for packaging or actually package the products, all while keeping the products organized in some fashion.
Typical examples of stacked products are food oriented products such as trays, plates, and cups. These products can be made of polystyrene and other plastics, paper, aluminum, or any other materials that have the desired combination of strength, weight, and cost. A typical product, such as a meat tray, can be produced by a press machine which stamps it from sheets of polystyrene material. The formed products are output from the press machine in one or more product lines of stacked products. In effect, the product line is an endless, self-replenishing stack of products with each product nested between the products on either side of it. Most frequently, the products themselves are oriented so that they are each resting on one edge, and the product line itself is substantially horizontal.
Handling stacked products in a product line as described in the above paragraph presents a number of problems. First, simply counting the products is a problem. Existing methods of counting products to obtain the desired number of products in a counted unit have proved to be unreliable, in that they tend to vary from the desired or predetermined number of products in the counted unit. The existing methods and apparatuses for counting stacked products have included attempts to count the products by the length of the product line or to count individual products in the product line using optical scanning or mechanical methods to count the individual products as the product line passes the scanner or mechanical counting device.
The methods and apparatuses described above require a high degree of uniformity in the size and shape of the products and in the stacking density of the product line to be successful in providing an accurate and reliable count of stacked products in the product line. The stacking density of the product line is the number of products per unit length in the product line. With most manufacturing machines and methods, there is a certain amount of variation in the size and shape of the products as they are produced, such as variation in the product thickness. In addition, this variation in size and shape can affect the nesting of the stacked product which, in turn, can vary the distance between the stacked products in the product line. Environmental factors, such as temperature and humidity, also can affect the stacked products and the stacking density in the product line.
Another problem with existing methods and apparatuses for counting stacked products is that the existing methods and apparatuses frequently have an accumulated error due to variations in manufacturing processes and in stacking density of the product lines. An accumulation of error results from the process of counting, be it electrical, optical, or mechanical, which can cause errors in the count to be repeated or even magnified. Accumulated errors can come from optical misreads with optical systems. Errors in electrical counting systems may come from varying voltages which change calibrations, or temperature and humidity causing variations in electrical components which also can cause changed calibrations.
Just as variations in the manufacturing process and changes in environmental factors can cause problems in counting the product, they also can cause problems in the separation and handling of the counted units. Most existing methods and apparatuses for separating products in the product line also require a high degree of uniformity in product size and shape, and in stacking density in the product line. Variations in the location of a product edge in the product line, thickness of the product, or distance between two products in the product line also can cause an incorrect number of products to be separated into the product unit. These variations in the product, product line, and product density also can cause physical jamming of the handling apparatus.
As illustrated by the above discussion there are a number of desirable features for a method or apparatus for handling stacked products in a product line. It would be desirable to have an apparatus for handling stacked products in a product line that would consistently count the stacked product in the product line correctly. It also would be desirable to have an apparatus that could provide consistent counts of stacked products in a product line despite variations in manufacturing process or environmental factors. In addition, it would be desirable to have an apparatus that could provide consistent counts of stacked products without accumulating errors from earlier counts. Further, it would be desirable to have an apparatus for handling stacked products in a product line that would separate the stacked products into counted units containing predetermined numbers of the stacked products. In addition, it would be desirable to have a method for handling stacked products in a product line which could consistently count the stacked products in a product line, and separate those products into counted units with a predetermined number of products in them, despite variations in manufacturing processes or environmental factors.
While the discussion herein relates to methods and apparatuses for handling stacked and/or nested products in a product line, it is not intended that the invention be limited to this situation. It will be obvious from the description that follows that the present invention will be useful in other applications with problems common to those described herein.